Pandora on my Roku 3 sounds great. Roku-->HDMI-->TV-->digital coax-->AVR-->3.1
The only downsides are (1) running my TV for Pandora, hooking something up to the AVR and then casting Pandora would make more sense. If I cared enough, and (2) the Pandora app sucks, I can't add tracks to a station or use a lot of other features. I guess it's good in a pinch.
I'm fine with Pandora on Roku. Spotify, on the other hand, stinks on Roku. They haven't updated the Roku channel is more than two years.